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5 Harmful Overfishing Practices and Types of Gear

As the global population continues to grow, so does our demand for fish-based protein. Developments in commercial fishing and upgraded gear have made it easier to harvest fish, but at what cost?

Advancements in commercial fishing technology and gear mean we have the ability to wipe out entire fish populations in a very short period of time. We now face a crisis where 80 percent of our fisheries, which have been fished sustainably for thousands of years, are either fully exploited or collapsing.

For example, ancient societies like the Romans used shoreline traps to harvest bluefin tuna, a fishery that remained sustainable for over 2,000 years. However, in the last 40 or so years, bluefin tuna have been fished almost to the point of extinction. Due to the overfishing of its breeding stock, the bluefin tuna population has been all but wiped off the planet. Unfortunately, this story is not unique.

Fishing technology has evolved to target species everywhere they swim, rather than in the migration patterns that historically brought them within our reach. When coastal fisheries were wiped out, we began targeting offshore fisheries. As those continue to be depleted, we’re starting to fish even deeper, bringing wasteful and indiscriminate practices with us.

1. Longline fishing

A longline is a single, very long fishing line that is dragged behind a boat. It has thousands of smaller branch lines attached and each branch line has a baited hook that’s used to lure and catch the target fish. Longlines can be used near the ocean’s surface or the seafloor, depending on the fish being targeted, and can stretch for as many as 60 miles.

While they pull massive yields, longlines also easily attract and hook a variety of marine life, including non-target species like seals, dolphins, sharks, rays, sea turtles, and seabirds. Even if these marine animals don’t take the bait, they can easily get snagged on a hook or become entangled in the line.

The non-target animals hauled up with the target species are called bycatch and dropped overboard already dead, dying, or gravely injured. Overfishing doesn’t just threaten target species, but any species that can be hauled up as bycatch.

2. Drift netting

Imagine a wall of netting so fine you couldn’t see it until you were caught in it. That’s exactly how drift nets work. Up to 30 feet tall and 30 miles long, a drift net is a free-floating net that’s either left to float in the ocean’s currents or is rigged with weights on the bottom and buoys on top that keep it suspended vertically in the water.

These nets are nonselective and produce extremely high volumes of bycatch. This is especially problematic in pelagic fisheries, where dolphins, whales, swordfish, sharks, turtles, tuna, squid, seabirds, and salmon are commonly caught. When these nets are lost or abandoned, they still continue to fish, becoming death traps for all types of marine life in a phenomenon called ghost fishing. Lost and abandoned fishing gear like this accounts for 10 percent of all ocean litter.

3. Trawling

Trawlers drag nets across the bottom of the seafloor to catch the marine life that lives on or near it. Commonly targeted species include shrimp, cod, rockfish, and flounder. Trawling is another unselective type of fishing that also produces incredibly high volumes of bycatch. Up to 90% of a trawl’s total catch can be bycatch.

Even more alarming, trawling also damages the seafloor, uprooting vulnerable deep-sea corals, seagrass beds, and other habitats that provide food and shelter to a variety of marine species. The habitat destruction caused by trawling can be permanently damaging to the marine ecosystem. An ocean without healthy coral reefs is not a healthy ocean.

4. Gillnets

A gillnet is a particular type of drift net made from a mesh of monofilament line (like what you’d see on a normal fishing pole), which means fish and other animals can’t see it. The holes in the mesh vary in size, depending on the species being targeted, and are designed to be just large enough for the fish’s head to fit through. When a fish is caught, it is trapped by the gills which means it can’t swim forward or backward to escape. These nets can be set at all different depths along the water column.

These nets are also indiscriminate and result in high volumes of bycatch. They entangle much larger, non-target species of marine life up to and including whales. The mesh netting can get caught arounds animals’ heads, fins, wings, and flippers and is so strong that it’s nearly impossible to escape from. Marine mammals drown when they are unable to escape to the surface for air. Animals that aren’t killed outright often suffer infection, mobility loss, or even limb loss when the thin, sharp net cuts into their flesh.

Gillnets are particularly dangerous to bycatch species. For example, gillnets are used in the Sea of Cortez to catch the totoaba fish, whose swim bladder is highly prized for its perceived medicinal value in places like China. However, these gillnets have decimated a species of porpoise called the vaquita. Despite a temporary ban in the small area of water they call home, it’s unlikely this species will recover; there are less than 30 of these animals alive today.

5. Purse-seine nets

Think of a purse-seine net like a ladies’ drawstring purse, where the pouch is filled up and the top is cinched shut. Now imagine one that’s 18 football fields long and two football fields deep. Fishermen use these nets to capture an entire school of fish in a single haul. Once the school is located, it’s encircled with net and the bottom is cinched, trapping the catch within the net. The net is then pulled alongside or onto the boat where the catch is collected.

When a targeted school of fish also attract non-targeted species like sharks, turtles, and dolphins, those animals can also be hauled in as bycatch. In the Eastern Pacific Ocean, dolphins and tuna frequently swim together and some fishermen use purse-seine netting to herd them both into a tight and easy-to-catch unit. While the dolphins are released before the catch is hauled onto the boat, there is still an impact on the dolphins that threatens their ability to recover. Mothers can be separated from calves during this process, which means the calves will die. High levels of stress caused by the chase can also cause pregnant dolphins to abort pregnancies and cause reproductive issues in the future. This practice has been banned in the US, which is why it’s important to look for dolphin-safe labels on any tuna you buy.

Marine protected areas and sustainable fishing practices can help end overfishing

Because many of these practices and gear are used in the international waters of the open ocean, where no single body has the ability to truly enforce protective regulations and quotas, commercial fisheries are often left to act in their own self-interest, which is rarely what’s best for marine life or the ocean. In the meantime, countries continue to debate the appropriate regulations while stocks continue to diminish and prices continue to rise.

By establishing marine protected areas, we can protect overfished and commercially important species from the impact of overfishing and create safe areas where their populations can recover. Not only does this maintain biodiversity and provide refuge for endangered and commercial species, it also provides areas where fish are able to reproduce and grow to their full size, which increases both the size and quantity of catches in surrounding fishing grounds. Ending overfishing is a win for fish, for commercial fisheries, and for global food security.

How you can help

Supporting sustainable local fisheries shows that there’s a demand for sustainably caught seafood. Seafood Watch is a program run by the Monterey Bay Aquarium that helps consumers make informed decisions about the sustainability of their seafood. You can also look for seafood products with labels from the Marine Stewardship Council and the Aquaculture Stewardship Council, who certify sustainable wild-caught and fish-farmed seafood respectively.

4Ocean Team

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